Synthesis of poly(3-hydroxybutyrate) based crosslinker for flexible polyurethane foams and its applications.

摘要

A novel bio-based cross-linker, 3-hydroxy-N,N-bis(2-hydroxyethyl)butanamide (HBHBA), synthesized by Metabolix, Inc. using ethyl-3-hydroxybutyrate (ethyl-3HB) and diethanolamine (DEOA) was used to prepare flexible polyurethane foams with high porosity, excellent mechanical strength, and with soft comfort feel yet high resiliency, an essential requirement for automotive seats and wheelchair cushions for orthopedic patients to provide fatigue proof seating. The crosslinker achieves these properties by allowing for a timely microphase separation of the hard and soft segments which the conventional cross-linker diethanolamine (DEOA) fails to do thereby leading to more closed cells. Lan et. al. [1] studied the structure-properties relations of molded flexible foams made with HBHBA and DEOA and found DEOA based foams to have 21% intact cell membranes vs. only 4% in the case of HBHBA foams.;However, by synthesizing the HBHBA cross-linker directly from Poly(3-hydroxybutyrate) (P3HB), the precursor of ethyl-3HB, the process can not only be made more economical but also pave way for synthesizing other P3HB-based chemicals such as polyols. The current work has been divided into 3 parts:;Part I: Evaluation of different melt process techniques to synthesize HBHBA via P3HB aminolysis .;P3HB is known to undergo thermal degradation above its melt temperature of 165°C by cis-elimination via formation of a six-membered ring intermediate. However, in the presence of a base, the P3HB oligomers and/or dimers, attain enough chain flexibility even at moderately low temperatures (30-70°C) to form the six-membered ring intermediate by the activation of the acidic methylene group. During the aminolysis of P3HB with DEOA, the nucleophilic amine besides attacking the ester group of P3HB to produce HBHBA, could also activate the acidic 13-H next to the ester oxygen making it susceptible to thermolysis to produce by-products such as 3hydroxybutyric acid (3HB acid), crotonic acid, and a crotonated amide product called N,N-bis(2hydroxyethyl)but-2-enamide (BHEBA). These by-products can be major deterrents in the molded flexible polyurethane foam process. To prove the above hypotheses about P3HB thermolysis in the presence of DEOA both at high and moderately low temperatures (90°C), melt processing techniques such as batch mixing, twin screw reactive extrusion, molecular weight reduction of P3HB using reactive diluents to react the resultant powdery masterbatches with DEOA via surface erosion have been utilized. These processes were explored as viable means to produce high quality HBHBA directly from P3HB aminolysis.;Part II: Validation of ethyl-3HB based cross-linker for use in Flexible Polyurethane Foams (FPFs).;An ASTM standard D7487 was used to validate the level of the cross-linkers HBHBA and DEOA (control), gelling catalyst, and surfactant in formulations that are used to prepare toluene diisocyanate (TDI)-based molded flexible polyurethane foams. This lab-scale validation was performed by pouring the reaction mixture of the premixed flexible foam components and TDI into an untreated 83 oz. SweetheartRTM paper bucket and measurement of specific events (cream time, top of cup time, free rise time, gel time, and overall stability in terms of collapsed or shrunk or stable foam) henceforth. External factors such as stirrer design, stirrer speed, method of premix preparation, temperature, and humidity that effect the foam stability were also evaluated.;Part III: Preparation of bubble-free cast elastomer using HBHBA .;Ethyl 3-HB-based HBHBA was used as a chain-extending hard segment in a polyether polyol and polymeric MDI system. HBHBA was used at different levels to observe the optimum level required to produce a bubble-free elastomeric sheet. Thermal, morphological, and mechanical properties were studied to see the extent of phase separation of soft and hard segments. The extent of hydrogen bonding was evaluated using Fourier Transform Infrared Spectroscopy. Other factors such as type of isocyanates, catalysts, trays used to prepare elastomer, cure temperature, etc. were also evaluated.;References: 1. Lan, Z., Daga, R., Whitehouse, R., McCarthy, S., Schmidt, D. 2014. Structure properties relations inflexible polyurethane foams containing a novel bio-based crosslinker. Polymer 55, pp. 2635-2644.